Roberts, 27, pitched the last six seasons (2010-15) primarily in the Rockies' Minor League system, going 22-10 with a 2.61 ERA in 216 appearances (two starts). He went 1-3 record with a 5.12 ERA this season for Triple-A Albuquerque, but appeared in only 23 games after spending time on the DL for left elbow inflammation.
He posted a 5.79 ERA in nine appearances this year with the Rockies.
The Rockies designated him for assignment Friday.
Todd Zolecki is a reporter for MLB.com. Read his Phillies blog The Zo Zone, follow him on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.